Vaccine Safety: What You Should Know

The United States has one of the best vaccine safety programs in the world. Scientists are constantly monitoring information from several sources for any clues that a particular vaccine may cause an adverse medical event, such as an allergic reaction.

The safety of vaccines is often a topic of media stories and blog postings. This attention may make you wonder, "How do we know our vaccines are safe?" In the United States, a number of safeguards are required by law to help ensure that the vaccines we receive are safe. Here are some important things to know about vaccine safety in the United States.

1. The safety of vaccines is thoroughly studied before they are licensed for public use.
   Clinical trials are conducted to evaluate the safety and effectiveness of a vaccine before it can be brought to market. Vaccines are first tested in laboratory studies and animal studies. If the results indicate the vaccine is safe, additional testing in people must be done before the vaccine can be approved by the Food and Drug Administration (FDA). More…

2. There is a strong system in place to help scientists monitor the safety of vaccines.
   Vaccine safety is a shared responsibility among the federal government, state and local health departments, other partners, and the public. To help meet this shared responsibility, government agencies and their partners have established several coordinated systems to monitor the safety of vaccines after they have been licensed for public use. These systems, such as the Vaccine Adverse Event Reporting System (VAERS) and the Vaccine Safety Datalink (VSD) Project, are used together to help scientists monitor the safety of vaccines. More…

3. Like any medicine, vaccines can cause side effects. However, serious adverse events from vaccines are rare.
   Side effects can occur with any medicine, including vaccines. Slight discomfort (such as pain at the injection sight) is normal and should not be a cause for alarm. Nearly 90% of adverse events following vaccinations are categorized as non-serious. Anyone who receives a vaccine should be informed about both the benefits and risks of vaccination. Any questions or concerns should be discussed with a healthcare provider. More…

4. Receiving combination vaccines or several different vaccines during one visit is very safe and offers the quickest protection again multiple diseases.
   It is very safe to receive several different vaccines during one visit. Scientific data show that this results in very few side effects. Similarly, studies show that combination vaccines (which combine multiple vaccines into a single vaccine) pose no greater risk for side effects than vaccines given individually, with few exceptions (such as the combined MMRV vaccine). These vaccines also are as effective in the combined form as they are when given separately. More…

5. You can play a role in monitoring the safety of vaccines.
   Anyone can submit a report to VAERS, a vaccine safety monitoring system managed by CDC and FDA. The report of an adverse event to VAERS does not mean that a vaccine caused the event. It only indicates that the event occurred after the vaccine was administered. Proof that the event was caused by the vaccine is not required in order to send a report to VAERS. More…

More Information

• CDC's Immunization Safety Office
• CDC's Advisory Committee on Immunization Practices (ACIP)
• CDC's National Center for Immunization and Respiratory Diseases
• Vaccines, U.S. Food and Drug Administration
• Hope Lives Here. The Children's Hospital of Philadelphia
• Vaccine Research, National Institutes of Health